Electroplating barrel with internal anode and cathode

ABSTRACT

An electroplating barrel having a rotary plating drum with one or more plating chambers containing anode and cathode electrodes to reduce the inter-electrode distance and thereby adapt the barrel to plating applications, such as aluminum plating, using a plating solution of relatively low electrical conductivity.

United States Patent [191 Lui [ 1 Nov. 26, 1974 ELECTROPLATING BARRELWITH INTERNAL ANODE AND CATHODE [75] Inventor: Kenneth Lui, FountainValley, Calif. [73] Assignee: TRW Inc., Redondo Beach, Calif.

[22] Filed: Dec, 26, 1972 [21] Appl. No.: 317,960

[52] US. Cl. 204/213 [51] Int. Cl C23b 5/78 [58] Field of Search204/213, 214

[56] References Cited UNITED STATES PATENTS 639,766 12/1899 Porter .l204/213 2,865,831 12/1958 Ransohoff 204/213 3,582,526 6/1971 Campana204/213 3,650,937 3/1972 Henig 204/213 FOREIGN PATENTS OR APPLICATIONS1,204,902 9/1970 Great Britain 204/213 Primary ExaminerF. C. EdmundsonAttorney, Agent, or Firm-Daniel 'T. Anderson; Donald R. Nyhagen; JerryA. Dinardo [57] ABSTRACT An electroplating barrel having a rotaryplating drum with one or more plating chambers containing anode andcathode electrodes to reduce the inter-electrode distance and therebyadapt the barrel to plating applications, such as aluminum plating,using a plating solution of relatively low electrical conductivity.

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ELECTROPLATING BARREL WITH INTERNAL ANODE AND CATHODE BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates generally tothe electrolytic deposition of metal, and more particularly to a novelelectroplating barrel.

2. Prior Art Electroplating barrels, or barrel platers as they aresometimes called, are used to batch plate relatively small work parts,such as bolts, nuts, screws, washers, rivets, and the like. Simplystated, such a plating barrel comprises a rotary plating drum having atleast one interior plating chamber for containing the work parts to beplated. The drum is rotated submerged in a plating solution while avoltage is impressed across the plating electrodes. As the drum rotates,the plating solution circulates through the plating chamber via passagesin the chamber walls, and the work parts undergo a tumbling motion. Thetumbling motion establishes random contact of the work parts with oneanother and with a cathode electrode in the barrel to effectelectrodeposition of the anode metal on the parts.

The prior art is replete with a wide variety of such plating barrels asevidenced by the following patents:

These and other prior art plating barrels have one disadvantage whichthe present invention overcomes. This disadvantage resides in the factthat the anode is located externally of the plating drum and is commonlysuspended in the plating tank some distance from the drum. The distancebetween this external anode and the cathode or cathodes within the drumis thus quite large. I l

Because of this large anode-cathode distance, the existing platingbarrels are ill-suited toplating applications which involve the use ofaplating solution having low electrical conductivity, such as aluminumplating with the aluminum hydride plating solution described in US. Pat.No. 2,651,608. The conductivity of this latter plating solution, forexample, is so low that plating current flow between the external anodeand internal cathode or cathodes of the existing plating barrels is verysmall. As a consequence, the plating time and hence costs are too highto warrant use of the existing plating barrels for such platingapplications, except in very special or unusual circumstances.

SUMMARY OF THE INVENTION The improved electroplating barrel of thepresent invention has a plating drum rotatable support on a frame. Thedrum contains one or more plating chambers for receiving work parts tobe plated. One wall of each chamber has an access opening with a closureor door which may be opened to insert parts into and remove parts fromthe chamber. The barrel has passages for circulating plating solutionthrough each drum chamber. In use, the plating drum is submerged inplating solution and rotated to tumble the parts in the drum while thesolution is circulated through the drum chambers.

According to a primary feature of the invention, each plating chamber ofthe plating drum contains both anode and cathode electrodes. The anodeof each plating chamber is exposed for contact by the plating solutionin the chamber but is shielded against contact by work parts in thechamber. The cathode of each plating chamber is exposed for contact byboth the plating solution and work parts in the chamber as the partstumble during rotation of the plating drum.

Location of both the anode and cathode within each plating chambersubstantially reduces the anodecathode distance and effects acorresponding increase in plating current flow for a given platingvoltage. This increase in current flow is sufficient to reduce theplating time and hence cost of a plating operation, such as the aluminumplating operation mentioned earlier,

'using a low conductivity solution to economically feasible values.Accordingly, the present plating barrel is particularly suited to suchplating operations. It will become evident as the description proceeds,however, that barrel is not limited to these plating operations and maybe used to advantage for virtually any barrel plating operationincluding those which use a high conductivity plating solution.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an end elevation of animproved plating barrel according to the invention;

FIG. 2 is a side elevation ofthe plating barrel;

FIG. 3 is an enlarged section taken on line 3-3 in FIG. 1; and

FIG. 4 is an enlarged half-sectionl taken on line 4-4 in FIG. 2. i

DESCRIPTION OF THE PREFERRED EMBODIMENTS but are shielded againstcontact by the work parts. The

cathode electrodes 22 are exposed for contact by both the platingsolution and the work parts as the latter tumble in the drum, wherebythe parts are plated with the anode metal.

As noted earlier and will be better understood from the followingdescription, this location of both the anode and cathode electrodeswithin the plating drum constitutes a major feature of differencebetween the present plating barrel and the plating barrels of the priorart. This internal electrode location reduces the distance between theanode and cathode electrodes and thereby achieves two importantbenefits. First, reduction of the interelectrode distance permitseconomically feasible use of the plating barrel for platingapplications, such as aluminum plating, which'involve a plating solutionof relatively low electrical conductivity. Secondly, reduction of theinterelectrode distance acplating solutions.

Referring now in greater detail to the illustrated plating barrel of theinvention, the plating drum 12 is a cylindrical drum having threeradially spaced cylindrical wall members 24, 26, and 28 concentricallyarranged about the rotation axis of the drum and generally flat end wallmembers 30, 32 joined to the ends of the cylindrical wall members. Thecentral opening through the innermost cylindrical wall member 24provides a passage 34 which, and radial passages 36 through thecylindrical wall members 24, 26 and 28, comprise part of the passagemeans 18 for circulating plating solution through the plating drum.Attention is direction to the fact the radial passages 36 are uniformlydistributed, with the spacing shown, over the entire surface area of thewall members, but only a few of the passages in each wall member havebeen shown. The three cylindrical wall members define therebetweenradially inner and outer concentric annular plating chambers 38, 40 forreceiving work parts to be plated. The center and outer cylindrical wallmembers 26, 28 have access openings 42 with closures or doors 44 whichmay be opened or removed to place parts in and remove parts from theplating chambers. The outer door is held in closed position within itsaccess opening by a door clamp 46. The inner door is secured to theouter door by sector shaped endwalls 44a for removal of the doors as asingle unit.

The innermost cylindrical wall member 24 comprises a pair of radiallyspaced electrical insulating sleeves 47, 48 and an intervening metallicsleeve 50. The center and outer cylindrical wall members 26, 28 eachcomprise center and radially inner electrical insulating sleeves 52 and54. Extending longitudinally of the plating drum 12 between and spacedlongitudinally about the sleeves 52, 54 are a plurality of metallicconductor bars 56 and intervening arcuate electrical insulating spacers58. Each conductor bar 56 carries a number of metalliccontact buttons 60each having a shank 62 which is press fitted in the bar and extendsradially inwardthrough the adjacent inner insulating sleeve 54 and ahead 64 on the inner end ofthe shank. Surrounding the central insulatingsleeve 52 of the center and outer cylindrical wall members 26, 28 is ametallic sleeve 66. An electrical insulating sleeve 68 surrounds themetallic sleeve 66 of the wall member 26.

The metallic sleeves 50, 66 of the cylindrical wall members 24, 26 and28 constitute the anode electrodes of the plating drum 12. The conductorbars 56 and contact buttons 60 of the cylindrical wall members 26, 28constitute the cathode electrodes 22 of the drum. It will be observedthat the anode electrodes or anodes 20 are located about the radiallyinner sides of the plating chambers 38, 40 and are exposed to theadjacent chamber through the passages 36 in the cylindrical wall members24, 26 for contact by the plating solution in the chambers. The radiallyouter insulating sleeves 47, 68 of the latter wall members shield theanodes against contact by work parts in the chambers. The cathodeelectrodes or cathodes 22 are located about the radially outer sides ofthe plating chambers and are exposed for contact by both the platingsolution and work parts in the chambers.

The plating drum end wall members 30, 32 are essentially identical andeach comprises axially inner and outer electrical insulating plates 70,72. Each outer plate 72 has an annular flange 74 about its edge whichprojects axially inward over and is sealed to the edge of its innerplate 70. Between the plates 70, 72 of each endwall is a metallicconductor plate 76. The conductor plate 76 of endwall member 30comprises the same metal as and is mechanically and electrically joinedby screws 78 to the anode sleeves 50, 66. The conductor plate 76 of theendwall member 32 comprises the same metal as and is mechanically andelectrically joined by screws 80 to the cathode bars 56.

Extending coaxially from the ends of the plating drum 12 are metallicbearing shafts 82. Each shaft has an inner hub 84 which is mechanicallyand electrically joined by screws 86 to the adjacent end wall conductorplate 76. The plating barrel frame 14 has an upper plate 90 whichextends across the top of the plating drum 12 and hanger arms 92 whichstraddle the drum endwise. These hanger arms carry electrical insulatingbushings 94 which rotatably receive the bearing shafts 82 to support theplating drum for rotation on its rotation axis. Attached to the upperframe plate 90 are rings 96 for attachment to a hoist cable by which theplating barrel 10 may be lowered into and raised from a plating tankcontaining plating solution.

The ends of the plating drum shafts 82 project beyond the hanger arms92. Rotatably mounted on the projecting shaft ends are metallic bushings98 which have sliding electrical contact with the shafts. Mechanicallyand electrically joined to these bushings are conductor rods 100 havingupper terminals 102 for connection to cables leading to a platingvoltage source (not shown). Conductor rods 100 are secured by brackets106 to the frame hanger arms 92 and serve to retain the bushings 98 onthe drum shafts 82. The bushings and conductor rods are covered with anelectrical insulating sheath or jacket 108.

Connected by elbows 110 to the bushings 98 are conduits 112. Thepassages in the conduits communicate to the passage 34 through the innerwall member 24 of the plating drum 12. Conduits 112 connect to a pump(not shown) for circulating plating solution from the plating tankthrough the drum.

In operation of the plating barrel 10, the work parts to be plated areplaced in the plating chambers 38, 40 of the plating drum 12. The barrelis then lowered into a plating solution and the motor 16 is energized todrive the drum in rotation. Rotation of the drum causes the work partsto undergo a tumbling motion in the plating chambers, therebyestablishing random contact of the work parts with one another and withthe cathode contacts 60 to effect plating of the parts with the metal ofthe anodes 50, 66. The anodes, when consumed, are replaced by removingthe ends of the plating drum.

As noted earlier, the present plating barrel is designed primarily forplating applications using a plating solution of relatively lowelectrical conductivity, such as aluminum plating with the aluminumhydride plating solution described in U.S. Pat. No. 2,651,608. Theexisting plating barrels are ill-suited to such plating applicationsowing to the location of the anode externally of the plating drum. Thisexternal anode location results in a relatively large distance betweenthe anode and cathode and a correspondingly small plating current flowbecause of the low conductivity of the plating solution. The platingtime is thus so long as to make it economically unfeasible to use theexisting barrels for anything other than very specialized platingapplicatrons.

This disadvantage of the existing barrels is avoided in the presentplating barrel because of the internal location of the anode and cathodewithin each plating chamber of the plating drum. The distance betweenthe anode and cathode is substantially reduced by this internal anodelocation and the plating current flow is correspondingly increased to apoint which permits aluminum plating and other plating operations usinglow conductivity plating solutions to be accomplished in reasonable timeand at a reasonable cost. It will be understood that for a plating drumof given size, this advantage of the present plating barrel is enhancedby increasing the number of plating chambers in the drum and therebyfurther reducing the distance between the anode and cathode of eachchamber. The anode and cathode arrangement also results in a superiormetal plate on the finished parts. While the plating barrel of theinvention is particularly suited to aluminum plating and other platingapplications using a low conductivity plating solution, the barrel alsomay be used for plating with high conductivity solutions. In theselatter plating applications, the advantage achieved by the platingbarrel is a substantial reduction in plating time.

While the invention has been described in connection with a platingbarrel having a cylindrical plating drum with two concentric annularplating chambers, it will be understood that the internal electrodefeature of the invention may be embodied in plating drums of othershapes and having other than two plating chambers and/or platingchambers of other than annular shape.

I claim:

1. An electroplating barrel for plating work parts comprising: a

a plating drum having at least one plating chamber for containing saidparts, means for placing parts in and removing parts from each chamber,cathode and soluble anode means within said drum adjacent each chamberwith said anode means exposed for contact by plating solution in thechamber and said cathode means exposed for contactby both platingsolution and work parts in the chamber, said cathode and anode meansbeing rigidly fixed to and forming structural elements of the drum;

means for shielding said anode means of each chamber against contact bywork parts in the chamber;

electrical terminals connected to said cathodes and anode means andaccessible externally of said drum for connection to a d-c voltagesource; and

means supporting said drum for rotation. 2. An electroplating barrelaccording to claim 1 wherein:

said anode and cathode means of each chamber are mounted on walls of thechamber. 3. An electroplating barrel according to claim 1 wherein:

each chamber has radially inner and outer walls relative to the rotationaxis of said drum; and the inner and outer walls of each chamber mountsaid anode and cathode means, respectively, of the chamber. 4. Anelectroplating barrel according to claim 3 wherein:

said inner and outer walls extend about said axis;

said anode means of each chamber comprises a metallic sleeve fixed tothe inner chamber wall;

said shielding means of each chamber comprises one electrical insulatingsleeve between said anode sleeve and the chamber; and

said cathode means of each chamber comprises metallic contacts fixed toand projecting into the chamber from the outer chamber wall.

5. An electroplating barrel according to claim 1 including:

means for circulating plating solution through each chamber includingpassages through the chamber walls.

6. An electroplating barrel according to claim 1 wherein:

said drum contains a plurality of said plating chambers.

7. An electroplating barrel according to claim 6 wherein:

said chambers are concentric annular chambers.

8. An electroplating barrel according to claim 7 wherein:

each chamber has radially inner and outer walls mounting said anode andcathode means, respectively, of the chamber.

9. An electroplating barrel according to claim 8 wherein:

said anode means of each chamber comprises a metallic sleeve fixed toand concentric with the inner chamber wall;

said shielding means of each chamber comprises an electrical insulatingsleeve between said anode sleeve and the chamber; and

said cathode means of each chamber comprise metallic contacts fixed toand projecting into the chamber from the outer chamber wall.

10. An electroplating barrel for plating work parts comprising:

a rotary plating drum having an axis of rotation, radi ally spacedannular wall members concentrically surrounding said axis, and wallmembers joined to the ends of said annular wall members to define acentral plating solution passage within the inner most annular wallmember and annular plating chambers between the adjacent: annular wallmembers, metallic bearing shafts secured to and extending coaxially fromsaid endwall members, closure means which may be opened to place partsin and remove parts from said chambers, and passages extendinglongitudinally through said shafts to said central passage and radiallythrough said annular wall members for circulating plating solutionthrough said chambers;

a frame having bearings receiving said shafts to sup port said drum forrotation on said axis;

said innermost annular wall member comprising a pair of radially spacedelectrical insulating sleeves and a metallic sleeve between saidinsulating sleeves;

each remaining annular wall member comprising a central electricalinsulating sleeve, a radially inner electrical insulating sleeve,metallic bars extending endwise of said drum between and spacedcircumferentially about the latter sleeves, metallic contacts fixed tosaid bars and extending radially inward through the adjacent innerinsulating sleeve into the adjacent plating chamber, and a metallicsleeve about said central sleeve;

each remaining annular wall member which separates two adjacent platingchambers further comprising an electrical insulating sleeve about therespective metallic sleeve;

each endwall member comprising a central metallic end plate electricallyjoined to the adjacent barrel shaft and electrical insulating platesenclosing said metallic plate;

said metallic sleeves comprising soluble anodes and said bars andcontacts forming cathodes;

means electrically joining one metallic end plate to said anodes;

means electrically joining the other metallic end plate to saidcathodes;

electrical terminals for connection to d-c voltage source; and

means electrically connecting said terminals and shafts, respectively.

11. An electroplating barrel according to claim 10 including:

means including a motor on said frame for driving said drum in rotation.

12. An electroplating barrel for plating work parts comprising:

a plating drum having a plurality of plating chambers for containingsaid parts, means for placing parts in and removing parts from eachchamber, cathode and anode means within said drum adjacent each chamberwith said anode means exposed for contact by plating solution in theadjacent chamber and said cathode means exposed for contact by bothplating solution and work parts in the adjacent chamber;

means shielding said anode means of each chamber against contact by workparts in the chamber;

electrical terminals connected to said cathodes and anode means andaccessible externally of said drum for connection to a d-c voltagesource; and

means supporting said drum for rotation. 13. An electroplating barre]according to claim 12 wherein: said chambers comprise concentric annular

1. An electroplating barrel for plating work parts comprising: a platingdrum having at least one plating chamber for containing said parts,means for placing parts in and removing parts from each chamber, cathodeand soluble anode means within said drum adjacent each chamber with saidanode means exposed for contact by plating solution in the chamber aNdsaid cathode means exposed for contact by both plating solution and workparts in the chamber, said cathode and anode means being rigidly fixedto and forming structural elements of the drum; means for shielding saidanode means of each chamber against contact by work parts in thechamber; electrical terminals connected to said cathodes and anode meansand accessible externally of said drum for connection to a d-c voltagesource; and means supporting said drum for rotation.
 2. Anelectroplating barrel according to claim 1 wherein: said anode andcathode means of each chamber are mounted on walls of the chamber.
 3. Anelectroplating barrel according to claim 1 wherein: each chamber hasradially inner and outer walls relative to the rotation axis of saiddrum; and the inner and outer walls of each chamber mount said anode andcathode means, respectively, of the chamber.
 4. An electroplating barrelaccording to claim 3 wherein: said inner and outer walls extend aboutsaid axis; said anode means of each chamber comprises a metallic sleevefixed to the inner chamber wall; said shielding means of each chambercomprises one electrical insulating sleeve between said anode sleeve andthe chamber; and said cathode means of each chamber comprises metalliccontacts fixed to and projecting into the chamber from the outer chamberwall.
 5. An electroplating barrel according to claim 1 including: meansfor circulating plating solution through each chamber including passagesthrough the chamber walls.
 6. An electroplating barrel according toclaim 1 wherein: said drum contains a plurality of said platingchambers.
 7. An electroplating barrel according to claim 6 wherein: saidchambers are concentric annular chambers.
 8. An electroplating barrelaccording to claim 7 wherein: each chamber has radially inner and outerwalls mounting said anode and cathode means, respectively, of thechamber.
 9. An electroplating barrel according to claim 8 wherein: saidanode means of each chamber comprises a metallic sleeve fixed to andconcentric with the inner chamber wall; said shielding means of eachchamber comprises an electrical insulating sleeve between said anodesleeve and the chamber; and said cathode means of each chamber comprisemetallic contacts fixed to and projecting into the chamber from theouter chamber wall.
 10. An electroplating barrel for plating work partscomprising: a rotary plating drum having an axis of rotation, radiallyspaced annular wall members concentrically surrounding said axis, andwall members joined to the ends of said annular wall members to define acentral plating solution passage within the inner most annular wallmember and annular plating chambers between the adjacent annular wallmembers, metallic bearing shafts secured to and extending coaxially fromsaid endwall members, closure means which may be opened to place partsin and remove parts from said chambers, and passages extendinglongitudinally through said shafts to said central passage and radiallythrough said annular wall members for circulating plating solutionthrough said chambers; a frame having bearings receiving said shafts tosupport said drum for rotation on said axis; said innermost annular wallmember comprising a pair of radially spaced electrical insulatingsleeves and a metallic sleeve between said insulating sleeves; eachremaining annular wall member comprising a central electrical insulatingsleeve, a radially inner electrical insulating sleeve, metallic barsextending endwise of said drum between and spaced circumferentiallyabout the latter sleeves, metallic contacts fixed to said bars andextending radially inward through the adjacent inner insulating sleeveinto the adjacent plating chamber, and a metallic sleeve about saidcentral sleeve; each remaining annular wall member which separates twoadjacent plating chambers further comprising an eleCtrical insulatingsleeve about the respective metallic sleeve; each endwall membercomprising a central metallic end plate electrically joined to theadjacent barrel shaft and electrical insulating plates enclosing saidmetallic plate; said metallic sleeves comprising soluble anodes and saidbars and contacts forming cathodes; means electrically joining onemetallic end plate to said anodes; means electrically joining the othermetallic end plate to said cathodes; electrical terminals for connectionto a d-c voltage source; and means electrically connecting saidterminals and shafts, respectively.
 11. An electroplating barrelaccording to claim 10 including: means including a motor on said framefor driving said drum in rotation.
 12. An electroplating barrel forplating work parts comprising: a plating drum having a plurality ofplating chambers for containing said parts, means for placing parts inand removing parts from each chamber, cathode and anode means withinsaid drum adjacent each chamber with said anode means exposed forcontact by plating solution in the adjacent chamber and said cathodemeans exposed for contact by both plating solution and work parts in theadjacent chamber; means shielding said anode means of each chamberagainst contact by work parts in the chamber; electrical terminalsconnected to said cathodes and anode means and accessible externally ofsaid drum for connection to a d-c voltage source; and means supportingsaid drum for rotation.
 13. An electroplating barrel according to claim12 wherein: said chambers comprise concentric annular chambers.